Answer:
A. Selection of the appropriate causal variable Y is important
Step-by-step explanation:
We have this function, Y = f(X).
From this function we can see that Y is dependent on X. That is, it is a function of X. Y is not a causal variable. A causal variable is a variable that is able to influence the variable of interest. From this question Y is the variable of interest. It is the dependent variable. The independent variable is X and it is the causal variable.
Therefore the incorrect one is Selection of the appropriate causal variable Y is important